Well I have spent a few hours today taking the car apart, drilling holes in it and putting it back together - I now have a functioning car PC!
I have replaced the BOSE head unit with a kenwood dpx501u double-din with AUX input wired up to the original BOSE speakers.
I have placed a 7 inch touchscreen where the sat nav cubby is normally and routed the 3 cables (power, vga and usb(for touchscreen) down behind the radio where they join up with the power/ground/ignition wires and from there through the center tunnel and back into the glove box behind the passenger seat - I had to cut out a small hole in the glove box liner tray to pass the cables through into the glove box.
The PC is an Epia SP13000 with slimine DVD drive, 40 GB hard drive, 512MB slimline RAM and all the normal ports; it's running windows xp and the shell I am using for the car PC is Centrafuse (this is software designed for a car touchscreen system). The PC is powered by an M2-ATX board, which is specifically produced for powering car PC and can handle up to 150W load. The M2-ATX supply can survive engine cranking and allows you to specify startup and shutdown delays (ie I have it set to start the PC 5 seconds after the ignition power comes on, and shut it down 45 seconds after it goes off - the PC then goes into hibernate ready to resume exactly where it was when you next start the car).
The PC has a bluetooth usb adapter which connects to bluetooth GPS and OBDII widgets.. the GPS enables me to have touch screen sat nav (using Destinator, built into Centrafuse), and the OBDII enables me to monitor various engine parameters and diagnostics (it plugs into the OBDII port just below the fuel cap release button). I also have a USB wireless keyboard with a little joystick-mouse thing - don't intend to keep it in the car but it's their if needed. Finally there is wireless LAN via USB again - this will enable me to connect to home network and sync files and also to connect to local hotspots.
I have taken a few pictures which I will post later.
The part that's left to do is to fit the screen into the dash properly - atm its just lying in the empty space where the nav cubby should go! This is reliant on me finding a 2003 nav cubby..